How to make div occupy remaining height?

Demo

One way is to set the the div to position:absolute and give it a top of 50px and bottom of 0px;

#div2
{
    position:absolute;
    bottom:0px;
    top:50px
}

Use absolute positioning:

#div1{
    width: 100%;
    height: 50px;
    background-color:red;/*Development Only*/
}
#div2{
    width: 100%;
    position: absolute;
    top: 50px;
    bottom: 0;
    background-color:blue;/*Development Only*/
}

<div id="div1"></div>
<div id="div2"></div>

You can use this http://jsfiddle.net/Victornpb/S8g4E/783/

#container {
    display: table;
    width: 400px;
    height: 400px;
}
#container > div{
    display: table-row;
    height: 0;
}
#container > div.fill{
    height: auto;
}

Just apply the class .fill to any of the children to make then occupy the remaining height.

<div id="container">
    <div>
        Lorem ipsum
    </div>
    <div>
        Lorem ipsum
    </div>
    <div class="fill">   <!-- this will fill the remaining height-->
        Lorem ipsum
    </div>
</div>

It works with how many children you want, no additional markup is required.

Since you know how many pixels are occupied by the previous content, you can use the calc() function:

height: calc(100% - 50px);